Re: low em wave shield

From: Edward Green (spamspamspam3_at_netzero.com)
Date: 09/08/04 

Date: 7 Sep 2004 20:14:43 -0700

Sam Wormley <swormley1@mchsi.com> wrote in message news:<MdUZc.24988$_g7.6658@attbi_s52>...
> Paul wrote:
>
>
> >
> > Some say, the cage will radiate whatever em wave that's inside the
> > cage and block what's outside? Can someone verify?
> > Since our world has lot of em waves and humans also radiate em waves,
> > does that mean, a human inside a cage will not receive em waves from
> > outside and outside world can receive some em waves from the cage?
> > Does the cage blocks all frequencies?
> > Does the cage have to be grounded?
> >
> > Thanks
>
>
> Faraday Cage
> http://scienceworld.wolfram.com/physics/FaradayCage.html
>
> A conducting cage used to shield electronic equipment. Amazingly,
> the law of electrostatics conspire so that electric fields outside
> are completely canceled out in the interior, as well as vice versa.

Quibble city:

The net charge inside the cage will certainly make itself felt outside
the cage (Gauss's Law).

Just what _is_ the correct statement of the modification of the field
of a charge enclosed by a conducting shell? We are given the shape of
one equipotential (the shell), and the surface integral of E on the
shell, or any surface enclosing it. On the shell itself the form of
the integral is particularly simple, since E is perpendicular to the
surface.

But is that enough to determine the field everywhere? I could produce
many fields with a given equipotential, but varying field strengths on
that equipotential. Is it enough if the space is free of other
sources? Do I need a further boundary condition at infinity?